GTypeClassCacheFunc to be called before the reference count of a
class goes from one to zero. This can be used to prevent premature class
destruction. All installed
GTypeClassCacheFunc functions will be chained
until one of them returns
TRUE. The functions have to check the class id
passed in to figure whether they actually want to cache the class of this
type, since all classes are routed through the same
This function is not directly available to language bindings.
Data to be passed to
The argument can be
The data is owned by the caller of the function.